This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The ultimate goal of our work is to understand how the brain functions. Because of the immensity of such an undertaking, it is only possible to study a small portion of brain function. We have chosen to study the output (motor) portion of brain function and we use the oculomotor system as our model system. Specifically, we study those fast movements known as saccadic eye movements. We continue our studies of mechanisms of saccade generation and have recently focused on the function of the caudal Fastigial nucleus (cFN), which is the output nucleus of the midline cerebellar vermis. Our studies consist of 3 related experiments to test what the function of the cFN is during the production of normal saccades. Specifically, we will use anatomical and physiological methods to test two hypotheses of cFN function;that of a feedback comparator that controls saccade amplitude versus an end-point controller that adjusts saccade amplitude in the face of unforeseen perturbations. Our anticipated results will change fundamentally, the way that we think saccades are produced. Not only will they improve our understanding of oculomotor processes but they may provide a new model for cerebellar function. If successful, the experiments will not only advance our understanding of how the brain processes information in order to formulate actions based on that information, but they are also basic to the differential neurological diagnosis based on eye-movement signs now commonly used clinically. Our results also provide a foundation for studies of more complex aspects of central nervous system function such as interactions between motor systems (e.g., eye and head during orientation) or sensory and motor systems (e.g., the visual and oculomotor systems) and more abstract functions such as attention.